MINNEAPOLIS (AP) — U.S. Agriculture Secretary Tom Vilsack said Monday that he's not ready to declare the Midwest bird flu outbreak over even though no new cases of the H5N2 virus have been detected over for over a month.

Poultry producers have caught a break thanks to the summer weather because warmer temperatures tend to kill the virus, Vilsack said in an interview with The Associated Press, but the threat hasn't passed.

USDA scientists believe waterfowl dropped the virus during the spring migration north, and they worry it could return this fall and potentially reach other regions, too, as temperatures cool and birds return south.

"We are very cognizant of the need to be prepared for a re-emergence of this in the fall in some parts of the country," Vilsack said.

Bird flu has cost U.S. poultry producers about 48 million birds, mostly egg-laying chickens in in Iowa and turkeys in Minnesota. The USDA probably will pay farmers close to $200 million in compensation and cover well over $300 million in cleanup costs, Vilsack said.

He also said his agency will discuss the lessons it has learned at a meeting next week in Des Moines, Iowa, with poultry groups. Topics will include the need to improve biosecurity and updates on the impact on poultry exports and efforts to develop a vaccine.

"There is still a very keen focus on this," he said.

Egg prices have soared because of hen losses in Iowa, the country's top egg-producing state, and elsewhere. Vilsack said the industry estimates it could take up to a year or so for the egg supply to return to normal — assuming no major resurgence of the virus.

"I think it's anybody's guess in terms of precisely how long it's going to take, but it's going to take a while," he said.